The present invention relates to a pixel-type two-dimensional image detector capable of detecting heavy particle beams such as, for example, alpha particle (particle beam having the mass heavier than the mass of proton) and neutron beam by using fluorescent materials in order to create two-dimensional images with much greater accuracy in associate with the incident beam intensity of heavy particle beam and neutron. The technologies for two-dimensional image detectors are useful for the space technology field as well as the nuclear technology field and the medical technology field.
Conventionally, as for the two-dimensional neutron image detector for heavy particle beams, more specifically, alpha particles, what have been used include a particle beam detector formed by combining a fluorescent material-based particle beam detecting sheet and a wavelength shifting fiber. As for the two-dimensional neutron image detector used for neutron scattering experiments using neutron sources generated by a nuclear reactor or an accelerator, what have been used include such a detector as being formed by combining a neutron-sensitive scintillator or a fluorescent neutron detecting sheet formed together with a fluorescent material and a neutron converter with a wavelength shifting fiber (refer to Patent Literatures 1 and 2, and Non-Patent Literature 1).
Such two-dimensional image detector is so configured that the position information may be obtained by using a cross-fiber reading method. What have been used include a cross-fiber reading method, including proven methods such as a method for determining the incident position by using a coincidence counting method using such a sheet configuration that a couple of wavelength shifting fiber bundles are arranged diagonally on the upper surface and the bottom surface of the fluorescent material sheet or the scintillator plate, a method for determining the incident position by using a coincidence counting method using such a sheet configuration that couple of wavelength shifting fiber bundles are arranged diagonally on the back surface of the scintillator by improving the cross-fiber reading method, and a method using such a sheet configuration that a couple of wavelength shifting fiber bundles are arranged diagonally and that scintillators are arranged on its upper surface and bottom surface (for example, refer to Patent Literatures 1 and 2, and Non-Patent Literature 1).    [Patent Literature 1] JP 2000-187007 A    [Patent Literature 2] JP 2002-71816 A    [Non-Patent Literature 1] Nucl. Instr. And Meth. , A430 (1999) PP. 311-320